1. Field of the Invention
The present invention relates to an improvement in a clutch mechanism mounted in a self-contained change speed apparatus for use on a bicycle.
2. Description of the Related Art
Conventional self-contained change speed apparatus, as disclosed in U.S. Pat. No. 5,078,664 and U.K. Patent application GB2166503A, employ a plurality of clutches in the form of pawl clutches and claw clutches and a clutch controller for providing multistage speeds. In these examples, operation of a shift lever is transmitted directly to the clutch controller. Consequently, a shift of the shift lever simultaneously results in a shift of the clutch controller with no substantial "lag" therebetween.
On the other hand, a drive torque is applied to engaging regions of a claw clutch, which acts as a resistance to disengagement of the claw clutch to impede smooth operation of the clutch controller. In the case of a bicycle, drive is variable with pedal positions, that is drive is weaker in upper and lower dead point regions for reasons of human engineering, with the result that diminished torque acts on the clutches. Consequently, only a minimum operating force is required for a smooth change speed operation if the clutches are operated when the pedals are in the upper and lower dead point regions. However, it is extremely difficult to operate the shift lever with such timing. Normally, therefore, a change speed operation is carried out with a great operating force overcoming a considerable resistance to disengagement. This involves an unsmooth clutch operation and shocks of shifting.
In the art of claw clutches, a spring or the like is sometimes incorporated into an individual clutch mechanism in order to avoid an overload. This results in a "lag" of the clutch controller, whereby the clutch is operated in a low disengagement resistance condition. However, the individual clutch mechanisms are not designed to cooperate with one another, nor are the clutches and springs. Thus, the addition of such springs makes little contribution to smooth operation of the change speed apparatus.